One class of new antifungal agents, the pseudomycins, shows great promise for treating fungal infections in a variety of patients. (see i.e., Harrison, L., et al., “Pseudomycins, a family of novel peptides from Pseudomonas syringae possessing broad-spectrum antifungal activity,” J. Gen. Microbiology 137(12), 2857-65 (1991) and U.S. Pat. Nos. 5,576,298 and 5,837,685). Pseudomycins are natural products derived from isolates of Pseudomonas syringae. P. syringae is a large group of plant-associated bacteria that have been the source of several bioactive substances, such as bacitracin and the syringomycins. Natural strains and transposon-generated mutants of P. syringae produce compounds with antifungal activity. A transposon-generated regulatory mutant of the wild type strain of P. syringae MSU 174, known as MSU 16H (ATCC 67028), produces several pseudomycins. Pseudomycins A, B, C and C′ have been isolated, chemically characterized, and shown to possess wide spectrum antifungal activity, including activity against important fungal pathogens in both humans and plants. The pseudomycins are structurally related to but are distinct from syringomycin and other antimycotics from isolates of P. syringae. The peptide moiety for pseudomycins A, B, C, C′ corresponds to L-Ser-D-Dab-L-Asp-L-Lys-L-Dab-L-aThr-Z-Dhb-L-Asp(3-OH)-L-Thr(4-Cl) with the terminal carboxyl group closing a macrocyclic ring on the OH group of the N-terminal Ser. The analogs are distinguished by the N-acyl side chain, i.e., pseudomycin A is N-acylated by 3,4-dihydroxytetradeconoate, pseudomycin B by 3-hydroxytetradecanoate, pseudomycin C by 3,4-dihydroxyhexadecanoate and pseudomycin C′ by 3-hydroxyhexadecanoate. (see i.e., Ballio, A., et al., “Novel bioactive lipodepsipeptides from Pseudomonas syringae: the pseudomycins,” FEBS Letters, 355(1), 96-100, (1994) and Coiro, V. M., et al., “Solution conformation of the Pseudomonas syringae MSU 16H phytotoxic lipodepsipeptide Pseudomycin A determined by computer simulations using distance geometry and molecular dynamics from NMR data,” Eur. J. Biochem., 257(2), 449-456 (1998).)
The present invention provides a group of pseudomycins which are particularly useful to protect plants and crops against fungal diseases.